Various methods have recently been tried to position an object (e.g. a writing tool) on a surface that has data or no data recorded thereon. Particularly, in connection with a positioning method using an electronic pen, a two- or three-dimensional positioning device for inputting graphic data (e.g. handwritten documents, symbols, drawings, etc) has become commercially available. Such devices convert the positional information, which has been sensed by position sensing means, into coordinates and determine the absolute position of the sensing means on a surface having data or no data recorded thereon.
A sensing means, such as a recording tablet, may be used to input handwritten data. Most two-dimensional devices are operated based on the contact between the recording tablet and the sensing means.
In general, there are two types of relationships between the sensing means and the recording tablet: passive sensing means/active tablet and active sensing means/passive tablet relationships, based on which the devices are driven.
In the case of the passive sensing means/active tablet mode, the active tablet is complicated, large, heavy, difficult to carry, and expensive. In addition, the active tablet is difficult to manufacture, and its complicated electric/mechanical structure makes it susceptible to erroneous operations (e.g. errors in position recognition).
In order to solve these problems, a device has been conceived to easily determine the absolute position of sensing means. The device includes a data recording surface provided with a coding pattern for determining the X-Y coordinate, a sensor for sensing the coding pattern, and a processor for determining the current position of the sensor based on the sensed coding pattern. The device, when driven, displays data on the computer screen when the user writes or draws, by hand, characters or image data on the data recording surface.
Exemplary coding methods by using such a device will now be described.
According to one of such methods, symbols are patternized for positional coding, as shown in FIG. 1. Particularly, each symbol consists of three concentric circles, the outermost one of them corresponds to the X coordinate, and the middle one corresponds to the Y coordinate. The outer and middle circles are divided into 16 portions, which indicate different codes depending on whether or not the interior of the circles is filled. This means that each coordinate pair is coded by complicated symbols having specific appearances.
In FIG. 1, reference numeral 1 generally designates a prior art positioning pattern structure in its entirety. Reference numeral 2 designates a single pattern structure of the entire positioning pattern structure 1. Reference numeral 3 designates a quadrant of the single pattern structure 2. Reference numeral 4 designates a center (as a reference point) of the structure 2. Reference numeral 5 designates a middle circle including information about a Y-coordinate and divided into sixteen zones. Reference numeral 6 designates an outermost circle having information about an X-coordinate and divided into sixteen zones. Reference numeral 7 designates a unit cell having information of X,Y coordinates in a single pattern (a cell pattern includes sixteen cells).
Another method employs a check pattern for coding X and Y coordinates in a manner similar to the above-mentioned method of using concentric circles.
Such conventional patterns have a problem in that, the more complicated and smaller symbols they consist of, the more difficult it is to realize patterns on the recording surface. If the sensing means has insufficient resolution, it may not accurately recognize fine patterns and result to erroneous positioning. If the pattern symbols are enlarged or simplified, the same pattern may be recognized in different positions on the recording surface. In such a case, redundant microcodes degrade the precision in absolute positioning. As a result, the position sensing means cannot accurately sense the position.